Undefined index.., Undefined offset.. warnings with WP_DEBUG

With define('WP_DEBUG', true); in wp-config.php some PHP warnings can be observed in a WordPress 3.4.2 and 3.5.1 admin backend, especially in combination with WPML plugin and its language switcher widget.

1. Warning on top of page /wp-admin/widgets.php:

Notice: Undefined index: icl_lang_sel_widget in ..wp-content/plugins/widget-logic/widget_logic.php on line 116